Search Results (4)

Desulfurized manganese residue (DMR) is an industrial solid residue produced by high-temperature and high-pressure desulfurization calcination of electrolytic manganese residue (EMR). DMR not only occupies land resources but also easily causes heavy metal pollution in soil, surface water, and groundwater. Therefore, it is necessary to treat the DMR safely and effectively so that it can be used as a resource. In this paper, Ordinary Portland cement (P.O 42.5) was used as a curing agent to treat DMR harmlessly. The effects of cement content and DMR particle size on flexural strength, compressive strength, and leaching toxicity of a cement-DMR solidified body were studied. The phase composition and microscopic morphology of the solidified body were analyzed by XRD, SEM, and EDS, and the mechanism of cement-DMR solidification was discussed. The results show that the flexural strength and compressive strength of a cement-DMR solidified body can be significantly improved by increasing the cement content to 80 mesh particle size. When the cement content is 30%, the DMR particle size has a great influence on the strength of the solidified body. When the DMR particle size is 4 mesh, the DMR particles will form stress concentration points in the solidified body and reduce its strength. In the DMR leaching solution, the leaching concentration of Mn is 2.8 mg/L, and the solidification rate of Mn in the cement-DMR solidified body with 10% cement content can reach 99.8%. The results of XRD, SEM, and EDS showed that quartz (SiO₂) and gypsum dihydrate (CaSO₄·2H₂O) were the main phases in the raw slag. Quartz and gypsum dihydrate could form ettringite (AFt) in the alkaline environment provided by cement. Mn was finally solidified by MnO₂, and Mn could be solidified in C-S-H gel by isomorphic replacement. Full article

Ammonia (NH₃) has received much attention as a hydrogen carrier because it can be easily liquefied with a high hydrogen storage density and emits no greenhouse gas during the dihydrogen evolution process. The ammonia oxidation reaction (AOR) in an electrochemical system has an important merit in which a very high-purity dihydrogen gas can be obtained without an additional separation process that is typically needed for thermochemical decomposition processes. Herein, the electrochemical AOR was carried out in a solid acid electrolysis cell (SAEC) at an intermediate temperature around 250 °C, in which a solid composite of CsH₂PO₄ mixed with SiP₂O₇ was used as an electrolyte and Pt/C-based electrocatalysts were employed as the electrode materials of both anode and cathode. The Pt/C electrode material was modified with the CsH₂PO₄/SiP₂O₇ electrolyte in order to enhance the electrocatalytic activity for the AOR with an improved H₂ production rate. Over the SAEC system reported here, a high AOR performance was obtained with a current density of 67.1 mA/cm² and Faradaic efficiency (FE) of 98.2%. This study can suggest the significant potential of SAEC for the carbon-free H₂ production from the selective electrochemical oxidation of NH₃. Full article

It is still a challenge to develop advanced materials able to simultaneously remove more than one pollutant. Exclusive cationic composite double- and triple-network cryogels, with adequate sustainability in the removal of Cr₂O₇²⁻ and H₂PO₄⁻ oxyanions, were developed in this work starting from single-network (SN) sponges. Chitosan (CS), as the only polycation originating from renewable resources, and poly(N,N-dimethylaminoethylmethacrylate) (PDMAEMA) and polyethyleneimine (PEI), as synthetic polycations, were employed to construct multi-network cationic composite cryogels. The properties of the composites were tailored by the cross-linking degree of the first network (SN5 and SN20, which means CS with 5 or 20 mole % of glutaraldehyde, respectively) and by the order of the successive networks. FTIR, SEM-EDX, equilibrium water content and compressive tests were used in the exhaustive characterization of these polymeric composites. The sorption performances towards Cr₂O₇²⁻ and H₂PO₄⁻ anions were evaluated in batch mode. The pseudo-first-order, pseudo-second-order (PSO) and Elovich kinetics models, and the Langmuir, Freundlich and Sips isotherm models were used to interpret the experimental results. The adsorption data were the best fitted by the PSO kinetic model and by the Sips isotherm model, indicating that the sorption mechanism was mainly controlled by chemisorption, irrespective of the structure and number of networks. The maximum sorption capacity for both oxyanions increased with the increase in the number of networks, the highest values being found for the multi-network sponges having SN5 cryogel as the first network. In binary systems, all sorbents preferred Cr₂O₇²⁻ ions, the selectivity coefficient being the highest for TN sponges. The high sorption capacity and remarkable reusability, with only a 4–6% drop in the sorption capacity after five sorption–desorption cycles, recommend these composite cryogels in the removal of two of the most dangerous pollutants represented by Cr₂O₇²⁻ and H₂PO₄⁻. Full article

A magnetite graphene oxide chitosan (MGOCS) composite microsphere was specifically prepared to efficiently adsorb As(III) from aqueous solutions. The characterization analysis of BET, XRD, VSM, TG, FTIR, XPS, and SEM-EDS was used to identify the characteristics and adsorption mechanism. Batch experiments were carried out to determine the effects of the operational parameters and to evaluate the adsorption kinetic and equilibrium isotherm. The results show that the MGOCS composite microsphere with a particle size of about 1.5 mm can be prepared by a straightforward method of dropping FeCl₂, graphene oxide (GO), and chitosan (CS) mixtures into NaOH solutions and then drying the mixed solutions at 45 °C. The produced MGOCS had a strong thermal stability with a mass loss of <30% below 620 °C. The specific surface area and saturation magnetization of the produced MGOCS was 66.85 m²/g and 24.35 emu/g, respectively. The As(III) adsorption capacity (Q_e) and removal efficiency (R_e) was only 0.25 mg/g and 5.81% for GOCS, respectively. After 0.08 mol of Fe₃O₄ modification, more than 53% of As(III) was efficiently removed by the formed MGOCS from aqueous solutions over a wide pH range of 5–10, and this was almost unaffected by temperature. The coexisting ion of PO₄³⁻ decreased Q_e from 3.81 mg/g to 1.32 mg/g, but Mn²⁺ increased Q_e from 3.50 mg/g to 4.19 mg/g. The As(III) adsorption fitted the best to the pseudo-second-order kinetic model, and the maximum Q_e was 20.72 mg/g as fitted by the Sips model. After four times regeneration, the R_e value of As(III) slightly decreased from 76.2% to 73.8%, and no secondary pollution of Fe happened. Chemisorption is the major mechanism for As(III) adsorption, and As(III) was adsorbed on the surface and interior of the MGOCS, while the adsorbed As(III) was partially oxidized to As(V) accompanied by the reduction of Fe(III) to Fe(II). The produced As(V) was further adsorbed through ligand exchange (by forming Fe–O–As complexes) and electrostatic attraction, enhancing the As(III) removal. As an easily prepared and environmental-friendly composite, MGOCS not only greatly adsorbs As(III) but also effectively removes Cr(VI) and As(V) (R_e > 60%) and other metals, showing a great advantage in the treatment of heavy metal-contaminated water. Full article